1. Field of the Invention
This invention generally relates to the field of catheters and more particularly to a catheter having a mechanism for retaining a distal end of the catheter in a predetermined configuration.
2. Description of Related Art
There are a variety of therapies or treatment modalities that require a catheter with a distal anchor or the like to retain the catheter in position. One particular application involves catheters used for drainage purposes. For example, procedures for the suprapubic catheterization of the bladder drain the bladder after surgery or when the genitourinary system is plugged by an obstruction. Procedures using other percutaneously inserted catheters are also used to drain the kidney or biliary system as well as to drain abscesses, other sites of fluid collection and other viscera. Still other procedures use percutaneously inserted catheters as gastrostomy feeding tubes.
Generally these catheters are introduced into a patient through a large hypodermic needle or trocar. A guidewire is inserted through the needle or trocar which is then removed. The catheter tube, with a stiffening cannula, passes over the guidewire into the cavity. The cannula and guidewire can then be withdrawn leaving a portion of the catheter at its distal end in the desired cavity.
It is very easy to withdraw one of these catheters by movement of the body or under other conditions. Also these catheters generally have side ports at the distal end that can be inadvertently drawn into the abdominal cavity creating potential for severe infections when the catheter is inserted for bladder treatment.
Various catheters have been developed with diverse anchor structures to prevent inadvertent removal of the catheter. One such anchor is a "pigtail loop" formed by a flexible tube portion at the distal end of the catheter. The loops have a number of ports to ensure drainage. The pigtail loop configuration prevents accidental removal of the catheter from the patient. Generally the pigtail loop is preformed in the catheter because the flexible tube of the catheter is formed of a memory material. For introduction into a patient, a stiff cannula or similar implement is inserted through the catheter lumen to straighten the pigtail loop. The distal end of the flexible tube returns to the pigtail loop configuration after the cannula is removed. Typically a suture thread extends through draw ports at two spaced positions along the distal portion of the flexible tube. These portions come into juxtaposition when the pigtail loop forms after the physician removes the cannula. Then the physician will take up any slack in the one or more suture threads that lead proximally from the pigtail loop. When a suture thread is made taut, it prevents the pigtail loop from straightening by holding the juxtaposed portions of the catheter together. If only a portion of the suture thread is drawn proximally, the suture thread will still prevent the pigtail loop from straightening completely.
When it is appropriate to remove the catheter, a stiff cannula is inserted through the lumen past the suture threads until the cannula reaches the pigtail loop. This minimizes the chances for the cannula entangling with the suture threads. Thereafter the suture threads are released and the stiff cannula is advanced distally to straighten the pigtail loop and facilitate the removal of the catheter from the patient.
With some catheters the proximal end of the suture thread is locked or retained in place by placing a hollow cap onto or over the proximal end of the catheter tube after the suture thread has been drawn into a taut condition. This structure traps the proximal end of the suture thread. Any protruding portion of the suture thread can then be cut if desired. Trapping or locking the suture thread prevents the pigtail loop from straightening.
With other catheters the suture thread is trapped between two or more hollow tubes one of which is slidably inserted axially into the other. A short length of suture thread is generally left hanging from the catheter so that if it becomes loose, it may be retightened. For example, U.S. Pat. No. 5,041,085 to Osborne et al. discloses a lockable sleeve drainage catheter with a flexible distal end that can form a pigtail loop. A locking sleeve positioned at the proximal end of the catheter draws the suture thread through a passageway to retain the distal end in the pigtail configuration. A locking collar at the proximal end of the elongated member tube has an annular recess formed therein. An annular step at the distal end of the lockable sleeve engages the recess to lock the sleeve in a fixed position. When fully extended and locked, the sleeve and elongated member form a fluid tight connection to prevent any leakage of fluids being drained.
U.S. Pat. Nos. 4,643,720 and 4,740,195 to Lanciano disclose alternative embodiments of a mechanism specifically designed for retaining the distal end of a catheter in a pigtail loop. As particularly shown in the later patent, a suture thread, as a flexible link, extends through a member that, when rotated, wraps the suture thread about the circumference thereof. Consequently after the distal end of the catheter forms the pigtail loop, rotating the member tensions the suture thread to prevent the pigtail loop from straightening.
U.S. Pat. No. 5,419,764 to Roll discloses still another structure that incorporates a twisting lock. The twisting lock is positioned at the proximal end of the catheter to draw the suture thread or flexible link through the passageway of the catheter after the distal end of the flexible tube forms the pigtail loop. Twisting the proximal member relative to the distal member of the twisting locking device causes the suture to wrap around a reel within the device. Once the locking mechanism tightens the suture thread and reaches its locked position, a rubber O-ring is compressed resulting in a fluid tight connection. The friction exerted between the O-ring and the adjacent members prevents unlocking of the system and unwinding of the suture thread.
Controlling steerable catheters constitute another class of catheters with deflectable tips that use suture threads as flexible links, but for steering purposes. For example, U.S. Pat. No. 5,030,204 to Badger et al. discloses an axially displaceable manipulator that displaces a control line to deflect a distal tip and decrease the included angle between the distal portion and main portion of a shaft. Thus adjusting the control line position enables the catheter to steer the catheter by deflecting the catheter tip.
U.S. Pat. No. 5,185,004 to Lashinski discloses another mechanism including a translational nut mechanism for limiting the number of turns that can be applied to a steerable guidewire. Stops to proximal and distal motion of the nut provide the limit.
Each of the foregoing Lanciano, Osborne et al. and Roll references discloses a locking or retention mechanism for maintaining the pigtail of a drainage catheter in a locked or retention position. However, each has certain disadvantages. For example, each of the retention mechanisms is formed as a housing with internally moving parts. The assembly of such mechanisms, particularly when it is desired to maintain a sealed environment, introduces complicated process or manufacturing steps that can increase the overall expense of the final catheter to prohibitive levels. Moreover, each involves locating a somewhat enlarged structure at the proximal end of the catheter that can be cumbersome to use and increase patient discomfort. Certain of these mechanisms are also subject to patient manipulation.